what i would do in your case is put about 5000 down, then leave the rest in that account to gain interest, pay 3 payments ahead,(out of that account), then just make the regular payments. (all out of that account). that way your money gains interest to kind of offset the interest you will be paying on the loan.
of course you should still deposit into that account, the same way you have been. ...in a perfect world... that would keep your payments up (or ahead), would share the interest burden with the bank..., and if it is strictly followed, then you should have a chunk of money in there left over when the car is paid off.
also the longer loan shows better on your credit for the future.
but since the world isnt perfect... lol and if yours is like mine. then you still have a good start, a good plan, and as long as you pay every month, you will have a 3 month safety net for emergency situations.